Polish women experience breast cancer incidence (BC) one third that of U.S. women (age-adjusted rates per 100,000 in 1990; Warsaw City 37; Warsaw Rural 18; and in 1985-9; U.S. whites 94). Yet, recent studies of Polish immigrants to the West showed BC mortality rates for immigrants similar to the rates of the host county (standardized mortality ratios 91 (US), 100 (Australia), and 97 (England and Wales). No other population of migrants has shown so rapid a transition. The short time needed to express this changing risk for BC implicates modifiable environmental factors as significant determinants of risk. To evaluate the role of these factors, characteristics of place of origin and destination, change in habits, and when these changes occurred, as well as the individual's characteristics that influence BC risk, must be assessed. We propose to conduct two parallel, population-based case control studies of 20-74 years old incident BC cases in two populations: 1) Polish-born Immigrants, (378 cases and 378 controls) residing in Cook County and Detroit Metropolitan Area and 2) Polish-native, (500 cases and 500 controls) residing in Warsaw City. We hypothesize that components of both usual and past diet are associated with BC risk. We hypothesize that after adjusting for established risk factors BC risk will be increased by: (1) reduction in intake of specific types of foods (e.g. cruciferous vegetables, sauerkraut, root vegetables, whole grain breads and other cereals), and thus: 2) reduction in intake of phytochemicals (e.g. glucobrassicins, carotenoids, flavonoids, and antioxidants), and dietary fiber; and 3) increase in intake of meat, meat products and dietary fat; and 4) interaction among the dietary constituents in 1-3 above. Assessment of dietary intakes at three points in life (late 1980'S, premenarcheal, premenopausal) will provide insight whether there are key ages when dietary factors alter BC risk. This study brings together disparate areas of BC research (nutrition, epidemiology, changes in risks due to migration) in strategically selected populations with 3 fold difference in BC mortality in order to develop critical understanding of the nutritional risk factors and their implications in BC etiology. The research team has extensive experience in the conduct of epidemiological studies and unique access to these populations. The proposed study will examine the role of emerging and established risk factors for BC and their interactions. Thus, results from this study should help clarify the ambiguous findings for dietary fat, and will contribute to understanding the role specific vegetables and phytochemicals play in lowering BC risk, with clear implications for BC prevention.